Thermostat

ABSTRACT

A thermostat wherein a pair of contact plates are inserted into a heat sensing cylinder. Ends of the contact plates are fixed at an end of the heat sensing cylinder and the other ends engage a contact plate tension member extending from the other end of the heat sensing cylinder. Due to difference in the heat expansion of the heat sensing cylinder and the contact plates caused from variation of temperature, the contact plates open or close the contact point. Setting of the temperature is accomplished by movement of the tension member by the use of a screw member. Means are provided for removing the backlash present in the screw members, whereby the thermostat is activated to operate accurately in conformity with the present temperature.

United States Patent Kondo June 26, 1973 THERMOSTAT Primary Examiner-Remard A. Gilheany [76] Inventor: Kenshi Kondo, No. 6-3 Seta-machi, Asslsmm Examfner F Tamagawa, setagaywku, Tokyo Attorney-Clano Ceccon Japan 221 Filed: Sept. 28, 1971 1 ABSTRACT Appl. No.: 184,428

[52] US. Cl. 337/392, 200/166 M, 337/400 [51] Int. Cl. 1101b 37/12 [58] Field of Search 200/158, 166 M; 337/392, 394, 398, 399, 400

[56] References Cited UNITED STATES PATENTS 2,257,990 10/1941 Turenne 337/392 1,920,713 8/1933 Prince 200/158 2,599,637 6/1952 Hutton 200/158 2,719,198 9/1955 Cunningham.... 337/392 2,698,367 12/1954 Poitras 337/398 A thermostat wherein a pair of contact plates are inserted into a heat sensing cylinder. Ends of the contact plates are fixed at an end of the heat sensing cylinder and the other ends engage a contact plate tension member extending from the other end of the heat sensing cylinder. Due to difference in the heat expansion of the heat sensing cylinder and the contact plates caused from variation of temperature, the contact plates open or close the contact point. Setting of the temperature is accomplished by movement of the tension member by the use of a screw member. Means are provided for removing the backlash present in the screw members, whereby the thermostat is activated to operate accurately in conformity with the present temperature.

1 Claim, 9 Drawing Figures PAIENIEDaunzs 191a 3.742.416

sum 2 or 2 l l -P-B INVENTOR.

THERMOSTAT INTRODUCTION This invention relates to a thermostat and more particularly to a thermostat operative through the difference in the heat expansion coefficients of two metals consisting of different materials.

THE PRIOR ART A thermostat has heretofore been known and extensively used wherein a pair of contact plates is inserted into a heat sensing cylinder and, due to the difference in the temperature-caused elongation of the heat sensing cylinder and of the contact plates, the latter are expanded or contracted so as to open or close a pair of contact points on the contact plates. In this arrangement, one terminal of each contact plate is fixed to an end of the heat sensing cylinder, while the other terminal is threadedly fitted into an aperture at the other end of the heat sensing cylinder and is engaged to a contact plate tension member projecting into the heat sensing cylinder. Upon turning of a screw member, the tension member advances or recedes, whereby the spacing between the engageable end of the tension member and the terminal of the contact plate can be changed and the contact point for opening and closing the circuit is altered. Thus, by rotation of the screw member, it is possible to change the temperature setting, which operate is simplified in practice by providing a knob at an end of the screw member and a graduated plate on the end surface of the heat sensing cylinder.

However, thermostats are not reliable to regularly open or close at a set temperature and this is particularly noticeable when the setting is effected at a high temperature or at a time when the thermostat is in operation and, after the setting, it is cooled and then heated again to a high temperature. In this case, the thermostat opens or closes at a temperature slightly at variance with the set temperature. Experimentally, it can be proved that when a number of thermostats of the same type are subjected to the changes above described and the observed temperatures are graphically plotted so as to represent a deviation distribution curve, only about 70 percent of thermostats lay within limits of :3C of the preset temperature (500C) and very rarely come within limits of ilC. At present, however, the demand for accuracy is very severe, when requires a temperature error so small as to be within at least 11C or better.

BRIEF SUMMARY OF THE INVENTION Applicants have made various studies on the cause of discrepancy between the working temperature and the preset temperature and have found that such discrepancy results from the backlash involved in the abovementioned screw member. They further ascertained that the presence of a twist in the contact plate upon expansion and contraction of the plate by temperature change is undesirable and that the relative movement of the heat sensing cylinder and contact plates should be precisely a correct linear movement.

It is, therefore, the main object of the present invention to provide a thermostat which can operate most precisely at the preset temperature.

It is another object of the invention to provide a thermostat which is capable of operating at the preset temperature so as accurately and most efficient remove the above described backlash.

It is a further object of the invention to provide a thermostat which performs most accurately at a set temperature by providing a means for assuring that the relative movement of the heat sensing cylinder and the contact plate is an accurate linear movement.

In accordance with the present invention, there is provided a thermostat which comprises a heat sensing cylinder, a pair of contact plates inserted at one end into said heat sensing cylinder, a contact plate tension member having an end portion threaded to be fitted into a screw hole at the other end of the heat sensing cylinder and projecting into the heat sensing cylinder to engage the terminals of the contact plates, and a spring member urging said tension member inwardly in the heat sensing cylinder thereby completely removing the backlash from between the screw hole and the threaded portion of the tension member.

The spring member is preferably a compression spring which may be inserted between one end of the contact plate and the end portion of the tension member. Preferably, the thermostat of the invention may be provided with an elongated member and a guide member for correctly guiding the movemember of said tension member.

THE DRAWINGS The invention may best be understood by reference to the following detailed description thereof taken in conjunction with the accompanying drawings in which:

FIG. 1 is a partly cutaway elevational view showing a construction of a thermostat according to the present invention;

FIG. 2 is an elevational view of the contact plates of the thermostat of FIG. 1, rotated FIG. 3 is a cross sectional view of the heat sensing cylinder of the thermostat of FIG. 1, rotated 90;

FIG. 4 is a cross sectional view taken along the lines A-A of FIG. 1;

FIG. 5 is a cross sectional view taken along the lines B-B of FIG. 1;

FIG. 6 is a perspective view of the guide plate member of a contact plate tension member;

FIG. 7 is a perspective view of a jig for welding an elongated member;

FIG. 8 is a graphic illustration of the backlash present in the screw portion; and

FIG. 9 is a partly cutaway elevational view showing a construction of a thermostat according to other embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIGS. 1 to 6 and particularly to FIG. 1, thermostat 1 comprises heat sensing cylinder 2 and a pair of contact plates 3, 3'. The heat sensing cylinder 2 is a metallic cylinder, one end of which is closed with bottom plate 4 and the other end is closed with cap 5. A screw hole 6 is bored in cap 5, which hole 6 is threadedly fitted with an outer screw 7. The outer screw 7 is made from a short tubing and is formed with a screw hole 8 on the inner surface thereof as best seen in FIG. 2. Upon the inner surface of the heat sensing cylinder 1, there is welded a pair of elongated members 9, 9' which are rectangular in cross section.

Contact plates 3, 3' consist of a pair of resilient sheets close to each other in the center and extending approximately parallel to each other at the ends. In the middle portion, these resilient contact plates are provided with insulating material 10, such as mica. There, contact bases 12, 12', having contacts 11, 11, are provided by caulking. Thus, contacts 11, 11' are fixedly connected to the contact plates 3, 3' and, through lead wires 13, 13 to an outside circuit. Contact plates 3, 3' are fixed at one end thereof by spot welding to contact plate fixing base 14, which is an integral part of or welded directly to bottom plate 4 which secured to one end of the heat sensing cylinder 2. Contact plates 3, 3 are also fixed by spot-welding at the other end thereof to contact plate fixing base 15, which is formed with a bore (not shown) in the middle thereof, through which bore contact plate tension member 16 is inserted. Traces of these spot-welded portions are shown at 17 and 18 in FIG. 1. The contact plate tension member 16 has at one end a threaded portion 19 and at other end referenced 16 a stepped portion 20 to which a guide member 21 is securely fitted. As seen best in FIG. 6, the guide member 21 is fixed at right angle with the tension member 16. Both end surfaces of the guide member 21 are arcuated to fit the curvature of the inner surface of heat sensing cylinder 1. Guide member 21 is also provided with recesses 22, 22 of rectangular shape. The recesses 22, 22' are adapted to receive the elongated members 9, 9 of the heat sensing cylinder so as to hold tension member 16 and contact plates 3, 3 in proper position. The threaded portion 19 of the tension member 16 is screw fitted into a hole 8 of the outer screw 7 as shown in FIG. 1. In accordance with the invention, a coil spring 23 is provided between the base and the guide member 21 at the end of the tension member 16.

In the thermostat as heretofore described, it is seen that when the ambient temperature rises the heat sensing cylinder 2 will expand more than the contact plates 3, 3, as the former has a larger heat expansion coefficient. As a result, a spacing d, FIG. 2, between the stepped portion of the tension member 16 and the plate 15 will decrease because the stepped portion 20 contacts the base 15. As the temperature rises further, the tension member 16 urges the contact plates to open contacts 11, 11'.

Thus, the temperature at which these contacts open, that is, the preset temperature can be controlled by proper adjustment of the spacing d. This adjustment of the spacing d can be effected by a turning of the outer screw 7. As previously described, when the temperature setting is made at a high temperature and, the thermostat has first cooled and is made then operative again under such high temperature, most thermostats will not open the contacts at this pre-set temperature, butwill operate at a temperature somewhat at variance with the pre-set temperature. This variance is caused by a backlash existing in the elements 6, 7 and 8, 19.

Turning now to FIG. 8, reference numerals 8 and 19 typically show screw hole 8 and screw threads 19. Assuming that the thermostat is set at a high temperature and then it is cooled, the heat sensing cylinder 2 would contract so that the threads 19 will move in the direction of arrow F1 and will reach the position shown by the solid line. If to the thermostat there is applied a high temperature, the heat sensing cylinder 2 will expand. As a consequence, the threads 19 will be moved to the position shown by the dotted line. The intevals between the positions shown in solid and dotted lines will constitute the aforementioned backlash which will hinder the efficient operation of the thermostat. It will be readily appreciated that this backlash will offset the temperature setting if the determination of the setting temperature by spacing d is taken into consideration.

The thermostat according to the invention uses a coil spring 23 which urges the tension bar 16 to cause the threaded portion 19 to always be in the position shown by the dotted line. The urging force of the spring is preferably 3 to 4 kg, whereas the force required for the opening of the contacts is 15 kg. It will not adversely affect therefore, the operation of the thermostat. The spring 23 also can provide a resilient connection between the free end of the contact plate at 15 and the free end of the tension bar 16, thus preventing the positional displacements of the contact plates, even when vibrations occur on the thermostat.

The surfaces of the rectangularly cross-sectioned elongated members 9, 9' are preferably of accurate configuration. They should closely register with the slots 22, 22' of the guide member 21. Accordingly, as a result the tension member 16 will make a correct linear movement when a temperature setting is effected and after the setting of the temperature has been done it will remain correctly in a stationary condition. Usually, the elongated members 9,9 are welded to the inner surface of the heat sensing cylinder 2. In welding, it is preferably to use a jig such as shown in FIG. 7. The jig 29 may comprise a cylindrical main body 30 of a diameter appreciably smaller than the internal diameter of the heat sensing cylinder 2 and an extended portion 33 of a diameter much smaller than that of the cylindrical main body. The main body 30 has two diametrically opposed slots 31 and 32, into which the elongated members 9, 9 are fitted with head portions slightly projecting (9 is not shown). The jig 29 is positioned in the heat sensing cylinder. To the extended portion 33 and to the portions on the outer surface of the heat sensing cylinder corresponding to the elongated members on the jig are provided lead wires, to which a high electric current is applied. In this manner, the elongated members 9, 9' can be securely welded to the inner surface of the heat sensing cylinder. Preferably, the material of the elongated member may be same as that of the guide member 21 so as to equalize their heat expansion coefficients.

An alternative arrangement of the present invention is shown in FIG. 9. In this embodiment, the spring which urges the tension member 16 toward the interior of the heat sensing cylinder is constituted of a coil spring 25 provided between a support arm 24 fixed on the tension member 16 and the cap 5. It is apparent that spring 25, similarly to the spring 23 is adapted for the removal of backlash. In FIG. 9, same parts as that of FIGS. 1 to 6 are shown by same numerals and, be cause their constructions and operations are essentially the same, a detailed description of the construction and operation of this second embodiment is therefore omitted.

While the invention has been described in detail with respect to certain now preferred embodiments, it will be understood by those skilled in the art, that variations and modifications can be made without departing from the spirit and scope of the invention, as given in the appended claims.

What is claimed is:

l. A thermostat comprising: a heat sensing cylinder having closed first and second ends: a pair of elongated contact plates in said heat sensing cylinder; a first base member attached to said first closed end of said heat sensing cylinder for securing one end of said contact plates to said first end of said heat sensing cylinder; a second, axially displaceable base member secured to the other ends of said contact plates; an adjusting screw mounted in said second closed end of said heat sensing cylinder; an elongated, rod like contact plate tension member having at a first end a terminal threaded portion screwed into said adjusting screw in said second end of said heat sensing cylinder, said tension member having an opposite stepped portion projecting into said member into the interior of said heat sensing cylinder. 

1. A thermostat comprising: a heat sensing cylinder having closed first and second ends: a pair of elongated contact plates in said heat sensing cylinder; a first base member attached to said first closed end of said heat sensing cylinder for securing one end of said contact plates to said first end of said heat sensing cylinder; a second, axially displaceable base member secured to the other ends of said contact plates; an adjusting screw mounted in said second closed end of said heat sensing cylinder; an elongated, rod like contact plate tension member having at a first end a terminal threaded portion screwed into said adjusting screw in said second end of said heat sensing cylinder, said tension member having an opposite stepped portion projecting into said heat sensing cylinder and coupled to said second base member; a pair of rectangularly cross sectioned elongated inwardly extending ribs integral with the inner surface of said heat sensing cylinder; an elongated guide member fixed to said stepped portion of said tension member at right angles thereto, said guide member having a notch at each outer end thereof for receiving said elongated members; and a compression spring extending about said tension member between said second base member and the transverse surface of said guide member opposed thereto for urging said tension member into the interior of said heat sensing cylinder. 